


Rise and Shine

by Teavat



Series: Ninety-Nine Problems (and being trans in a stone world is not one of them) [3]
Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: But all's well that ends well, Canon Compliant, Friendship, Gen, Isolation, Resilience, Senku fact-drops all over the place, Senku is like five kinds of incongruous moods and so is this fic, Senku is trans, Trans Male Character, about chemistry and bat viruses and what have you, and has a couple of breakdowns, boy scientist restarts civilization, contents of Senku's head ahead, fails a lot while at it
Language: English
Status: Completed
Published: 2020-04-14
Updated: 2020-04-16
Packaged: 2021-03-02 00:36:00
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 15
Words: 18,615
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23656216
Author URL: https://archiveofourown.org/users/Teavat/pseuds/Teavat
Summary: Senku may be clever, resourceful and persistent, and he may have a phenomenal repository of science facts at his disposal, but he's still only a single, lone human in a great big world. The (slightly less than) six months he spends alone in the stone world teach him a few things about priorities, human nature and the value of company.
Series: Ninety-Nine Problems (and being trans in a stone world is not one of them) [3]
Series URL: https://archiveofourown.org/series/1703308
Comments: 28
Kudos: 123





	1. The Progress Log of A Boy Scientist Extraordinaire

**Author's Note:**

> Additional notes and content warnings for each chapter will be in the end notes.

**Summary for the Chapter:**

> April 1st 5738, day one: On my first day after breaking out of stone, I acquired basic stone tools and a reliable access to combustion using the bow drill method. I also learned that I’m shit at spinning a stick, and that I shouldn’t hit myself with a rock, because that hurts.

_Seven, eight, nine, ten. One, two, three._

_It’s spring again. Time to get up. Get up._

This isn’t going to work. After 3718 times, there’s only a couple of promilles’ chance that it might.

_Four, five, six._

It beats doing nothing, though. And it isn't counting.

_Come on, Senku, get up._

_Seven, eight, nine. One, two, three, four._

_Get up. GET UP—_

_**CRACK.** _

-

One Senku Ishigami – teenager, show-off, Science Club President, pack-rat, aspiring astronaut, amateur engineer, space nut, Doraemon fan, member of a gender minority and a video game aficionado – is possibly the first human being to walk on the planet in slightly under 3,719 years.

There’s nothing around him that suggests civilization has survived. If someone else had already figured out how to get out of stone, there ought to be at least some signs of human life. Yet it’s just him and a bunch of curious monkeys, in a sea of green that goes on as far as the eye can see.

All the limitations on what he can do – when, where, in which order, with whom, and with what credentials – are gone. There will be no more awkward conversations with his dad after watching the evening news report another mysterious blip in the city airspace. Materials will be harder to come by and everything has to be made from scratch, but every single scientific and technological invention he recreates from this moment onwards, no matter how mundane or small, is a true achievement.

He’ll bring the world back. He’ll bring it _all_ back. With knowledge and perseverance, you can do anything. All the wonders of civilization and technology hover at his eager fingertips, just waiting to be grasped.

-

His eager fingertips do not appreciate his inability to bang rocks together without getting them caught in between.

He imagines jotting that down in a personal log.

_April 1st 5738, day one: On my first day after breaking out of stone, I acquired basic stone tools and a reliable access to combustion using the bow drill method. I also learned that I’m shit at spinning a stick, and that I shouldn’t hit myself with a rock, because that hurts._

Once everything is back up and running, maybe someone will write a biography of him. Getting his own scientist biography would be incredibly cool. He should file away all his best quips, so that he can use them when he's interviewed. Come to think of it, if someone _does_ write a biography of him, no one is ever again going to be able to say that only cis people make history. _Trans boy brought the world back_. Take that, haters.

He laughs about it as he sits by the fire he made with his own two hands, his wit and his effort, and holds his sore hands close to its heat. An hour later, when his fingers start to swell, he remembers that you should treat crush injuries with _cold_.

-

_Senku’s headspace log, April 2nd 5738, day two_

_Rain sucks. Waking up to being rained on while naked sucks more. The damp cave that smells like moss and bat droppings sucks too, but slightly less. It's cold and I’m hungry and this place is probably teeming with potentially zoonotic pathogens. The fact that I'm sitting in it and not wearing any kind of protective gear would make my erstwhile filovirus research team leader wring her hands with anxiety. Once I pick a place to live in, I want a healthy distance between that and this cave, and also anything that I eat._

_Acquired: dead squirrel with claw marks in its side, so probably not very diseased  
_ _Add sputtering, smoking fire  
_ _Acquired: extra charred dead squirrel with some edible bits in the middle  
Hopefully not acquired: bat diseases  
_

_Note to self: dripping wet moist wood resists friction-based ignition even better than mostly dry moist wood. Need to stack firewood in a dry place._

_Senku’s headspace log, April 3rd 5738, day three_

_My androgen implant seems to have survived petrification, though I’m not yet sure whether it’s still working or not. How it’s been affected is interesting, because it was inside my body during the petrification and it’s a non-biological object. Sadly there’s no way to do blood tests here. My tooth fillings seem to be okay, and clearly none of the complex molecules in my body have deteriorated because all of me still works, so there’s a good chance the implant is fine, too._

_That bodes well for people with replacement parts. If the petrification had affected non-biological parts of the bodies differentially – or if complex molecules broke down over time while you were petrified... on the second thought, let's not go there._

_Senku’s headspace log, April 5th 5738, day five_

_The monkeys keep sneaking up to stare at me. Take note, fellow primates: you can start a competing civilization if you get on it quickly enough. Or we can go back to that thing where you poke at my stuff and steal my trash and we share hot springs in winter. That works for me, too._

_Up next: clothes!  
_ _Require: animal hide  
_ _Most efficient source available: deer_

_Senku’s headscape log, April 6th 5738, day six_

_Deer are fast. Humans are supposed to be fearsome pursuit predators with incredible stamina compared to other species. Whoever said that hadn’t met me._

_On the other hand, I have rope. Fear me, deer._

_Senku’s headspace log, April 7th 5738, day seven_

_I have found a copse of trees that is teeming with leeches. The leeches were discovered after I sat there for two hours, keeping watch on an animal trail. Leeches like warm, moist spots where the skin is thin. I was sitting down. The posterity can do the math for itself._

_I’ve never been out camping, and I used to think that leeches were interesting. I’ve changed my mind. Leeches are not interesting. Up close and personal, leeches are fucking atrocious little abominations. If I find a tobacco plant, I will build a whole orchard with nothing but tobacco in it and live in the middle, I will soak everything I wear in an infusion of tobacco, and once I get sodium chloride, I will salt the ground wherever I walk._

_On the bright side, if I ever need to reattach a severed finger or toe and figure out how to sew up an artery, I’ll know where to get something that can take the extraneous blood out while the veins grow back together._

_Senku’s headspace log, April 8th 5738, day eight_

_I have now tested five different kinds of traps that don’t work. I’ve also used my stone tools to make a pile of more or less straight planks while waiting to see whether the traps will work. I think the muscles in my arms and back are dying._

_Senku’s headspace log, April 9th 5738, day nine_

_I have found a type of trap that works! My rope, however, does not. I need a sturdier rope._

_Deer is laughing at me. Don’t at me, deer; I_ will _get you._

_Senku’s headspace log, April 11th, day eleven_

_I know what I’ll do with my lumber: I’ll build a tree house. Being off the ground provides additional safety from any potential big predators and vindictive family members of deer that might be around. A tree house might also contain fewer spiders and leeches, and it’s dry and flood-proof. It's ideal for a variety of compelling reasons._

_I’ve also always liked the idea of tree houses, even if I've never had a use for one before. What better time to finally make one than when you're stuck in a new stone age.  
_

_Senku’s headspace log, April 12th, day twelve_

_Nails, hammer, drill? I wish. There’s no hardware store to go to, no familiar-as-the-back-of-my-hand tool pack in the cupboard, no power tools in dad’s garage. Stone knife and wood joinery it is_.

_Note to self: fastening the lumber at both ends when I'm winching it into the tree lessens the likelihood of dropping it onto my own head._

_Senku’s headspace log, April 13th, day thirteen_

_Once I get the deer, that’ll give me bone glue to attach the roof with. Grind bones into a fine dust, dissolve the dust in water, let the water evaporate until you get jelly and you’re done! All you need to do is plaster it on and wait for it to dry.  
_

_Goal: shelter that doesn't have bats in it  
Need: bone glue  
_ _Source: that damn deer  
_

_Senku’s headspace log, April 14th 5738, day fourteen_

_I have conquered the deer! The deer is no longer laughing! Clothing and shelter, coming up!_

_Note to self: Rope needs to be fastened further away from the trap. Deer are damn heavy; getting crushed by one would be a mortifying end to Civilization 2.0._

_Senku’s headspace log, April 15th 5738, day fifteen_

_I found a leech in my tree house. It came with the deer. It definitely, ten billion percent, came with the deer._

_If it didn’t come with the deer I will move into the cave, pathogens be damned._

_Senku’s headspace log, April 18th 5738, day eighteen_

_I have chewed on raw deer hide that I’ve treated with deer brains and my own piss. Nothing scares me any more._

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- Brief speculation on petrification-related body horror  
> \- Mentions of zoonotic diseases carried by bats  
> \- Non-explicit animal death (as seen in canon) and non-explicit mentions of using the animal's parts and urine to make things (as to be expected in canon)  
> \- A close encounter with mountain leeches
> 
> I tried to look it up and there’s a chance that nobody actually chewed leather, like, ever. Oh, Senku, honey. There had to be something that you got embarrassingly wrong.


	2. Whoever (Re-)Invented Ceramics Didn't Do A Very Good Job

**Summary for the Chapter:**

> Senku makes his first chemical compounds. It involves pottery, which proves to be a headache.

**Notes for the Chapter:**

> Remember how, when they were making gunpowder, Senku just pulled out that bag of potassium nitrate out of his back pocket?

Acquire stone tools. Acquire fire. Acquire food. Acquire simple clay pots. Acquire shelter. Acquire clothing.

Senku arranges things as separate steps in his head to keep track of his progress. Basic survival necessities come first. Once he has those, he can build on them to make more complex things. Fire provides warmth, but it’s also good for cooking, scaring off big animals and producing aldehydes for preservation by smoking, and it leaves behind coal to use for filtering drinking water and ash that can be turned into lye. The animals he traps for food provide leather for clothes and other uses, but also tendons for string and fishing line, and bone for glue, tools, fertilizer, and making calcium phosphate and derivatives of phosphorus with. It isn’t much yet, but it’s a start. Every day, he adds something new to his growing list of resources.

The bat guano in that cave where he fled the rain is also an interesting material. It’s loaded with calcium and phosphorus, and with the pathogens removed, it would make for a good fertilizer, too.

Come to think of it, soaking guano in water and then filtering out the solids and precipitating the dissolved salt should get him potassium nitrate. Potassium nitrate is a pretty handy chemical: besides also being a fertilizer in its own right, it cures meat and softens up legumes, grains and other tough foods if added to them while cooking. It would be a good addition to his stone age kitchen. It’s one of the easiest things to make around here, too, so maybe he should get on that.

Potassium nitrate also a potent oxidiser that’s used in fireworks and black powder, and it so happens that it’s also a potential rocket fuel component. Not that he’ll be building a rocket for a while yet, but it’s something to consider.

To make potassium nitrate, he will need a vessel that can hold water better than his unfired clay pots, wooden bowls or leather bags can. He could try using bone glue to seal a woven bark basket or one of his clay pots to make it watertight, but that seems like a lot of trouble for an uncertain result, and there’s better uses for that bone. On the other hand, there is plenty more clay by the river, and plenty of rocks to build a kiln with.

Next goal: waterproof ceramics.

-

_Senku’s headspace log, April 29th 5738, day twenty-nine_

_A question: How do you make a kiln that doesn’t spout smoke all over the place and then collapse in on itself?_

_Senku’s headspace log, May 1st 5738, day thirty-one_

_Bricks ought to be a better building material than river stones. For bricks I need a firing pit. For a firing pit, I need a shovel._

_These things actually work out a bit like flowcharts, come to think of it._

_Start with: a shovel  
_ _A shovel leads to firing pit  
_ _A firing pit leads to bricks  
_ _Bricks lead to a kiln  
_ _A kiln leads to fired pottery, which leads to goal: a pot that holds water  
_

_Senku’s headspace log, May 2nd 5738, day thirty-two_

_Still haven’t learned how not to get my fingers caught in between a rock and a hard place._

_Acquired: shovel  
_ _Acquired: firing pit_

_Senku’s headspace log, May 8th 5738, day thirty-eight_

_Acquired: fired bricks  
_ _Acquired: kiln_

-

Pottery is _not_ easy. He should have figured that out from his experience with the stick and the chert. So far, every single one of his attempts has cracked while he tried to burn it. If only he had read _one_ book in his life about how to work clay.

If only he had scissors. If only he had a vacuum filter. If only he had a mail order account with infinite credit at a hardware-slash-chem store that had somehow survived for four thousand years.

Come on, Senku, whip up another pot. You can do it! People figured this shit out at least 30,000 years ago. 

Perhaps letting the clay out dry out longer before firing it will make a difference? Or mixing in something else, like sand?

-

_Senku’s headspace log, May 27th 5738, day fifty-seven_

_I have finally produced a fired pot. It is ugly as hell, but it is fired, and it is a pot. It stays upright, it keeps its shape, and it holds water. Waterproof ceramics acquired! I have levelled up in pottery!_

_Senku’s headspace log, May 28th 5738, day fifty-eight_

_Correction: waterproof ceramics_ not _acquired  
_

_The pot holds water for a limited stretch of time, which is definitely too short for evaporation, or even the twenty-four hours of soaking. Am also considering retracting that skill level-up._

_Heating the clay to well over 1,200 Celsius degrees would morph its chemical structure and give me some solid stoneware, but there’s no way I’m getting that kinds of temperatures out of this little kiln. So what else can I do?_

_That’s right – I can coat it with a glaze. A glaze coats the clay's surface and makes the pot watertight without vitrifying the entire pot into a glass. But doesn’t it require minerals? I'll need to take another look at those river stones.  
_

-

He has spent the entire day hauling rocks into his clearing, and he is starving. Even with the ravenous hunger, the dark leafy vegetables in his wooden bowl still taste bitter. It's not much of a comfort that it means there's more nutrition in them, especially since that nutrition doesn't include high amounts of calories. A dash of oil, or even a pinch of salt, would make them about ten billion times more palatable— _salt!_

Europeans used salt as pottery glaze. He read that once, when he was home sick, bored out of his head and endlessly clicking through wikipedia articles. Sodium chloride reacts with clay and forms a solid layer of sodium silicate that stops liquids from getting through. He should be able to get salt by evaporating seawater in a leather bag.

Looks like he’s going to the beach.

-

He finds one of the stone swallows by chance while he’s hiking down the river towards the coast. It’s in remarkably good shape, even after almost 4,000 years: it looks like it was sitting on a branch when it was petrified, and it still has its feet, with only a single toe missing.

He wedges it into one of his bags and takes it with him. Easily portable test subjects will come in handy later.

-

_Senku’s headspace log, June 3rd 5738, day sixty-four_

_I’ve located a very nice sandy beach and set up shop. I almost even caught a fish, but in the end had to settle for some mussels.  
_

_Note to self: Setting the wooden tripod for the cooking bag too close to the flame has the unfortunate side-effect of the wood catching on fire and the whole thing toppling into the flames. Instead of salt, the result is salty wet ashes. If there’s a use for those, I haven’t heard of it yet._

_Senku’s headspace log, June 5th 5738, day sixty-six_

_Acquired: salt  
_ _Also acquired: bonus ability to immediately get rid of crawly blood-sucking abominations anywhere, at any time, without building up a fire_

_Coming up: ceramics, level 3._

-

His first salt-glazed pot looks like it’s made of partially decomposed citrus peels. He’s seen nicer-looking results in a kids’ crafts class. But the pot doesn’t leak. It’s his very own, first ever, Senku-made waterproof container. He's proud of it. He’s so damn proud that when he makes a second one, he carves a scribbly likeness of his own face into its side.

He has finally figured out waterproof ceramics, and it only took six weeks.

Now that he knows how to do it, he can make a wide, shallow vat to evaporate brine in, which means that the damned wet-salty-ashes-producing cooking bag rig can finally go.

-

_Senku’s headspace log, June 19th 5738, day eighty_

_I cleaned out the kiln and noticed an interesting sheen on the inner walls. I can’t believe I forgot that wood ash can also be used as glaze. Wood ash is so much easier to obtain than salt. Maybe my old culture teacher was right when she said that I should have taken non-science lessons more seriously._

_On the upside, I now have lots of salt. Time for some fun seasoning and food preservation experiments!_

_Oh, and I almost forgot: potassium nitrate acquired!_

-

His ugly waterproof pots mean that he now has two crucial food additives that double up as mineral supplements and make things taste better and stay edible longer. Good work, Senku. He can also start storing up food outside the treehouse without having to worry about it getting waterlogged or eaten, which should free him more time to think about what to make next.

It’s exhilarating to witness first hand how one achievement opens up several new avenues. Making one thing gives you access to other things that you couldn’t reach without it. He already knew that science and civilization worked like that, but making things from scratch really drives it home in a way that reading about it from a book never did.

It’s like he’s playing a game that lets him level up and gain new skills. It turns out that video games provide surprisingly good analogies for human progress.

Just for fun, he takes some of the potassium nitrate he made, dissolves, filters and recrystallises it a few more times to take out most of the impurities, and stuffs it in a roll of bark with some ground-up charcoal. Then he throws the roll into fire and quickly backs out of range. The resulting bright burst of sparks leaves spots dancing in his vision.

After those spots clear up, he climbs to the roof of his tree house and lies down to watch the stars. He thinks for a moment that he can make out a satellite flash, but then he dismisses it as a lingering afterimage on his retinas. After almost four thousand years, everything that was in the low earth orbit will have decayed into the atmosphere and burned up. The only thing that should still be up there is the scrap in the graveyard orbits. Like the SNAP-10A, an American nuclear satellite from the 1960s with a crapshoot experimental ion thruster, which had actually been projected to stay where it was for four thousand years. Perhaps one day he can find it and restore it. Of course, he could also find a cloud of radioactive debris, but the possibility is still exciting.

His little popper with its impure oxidizer and rudimentary fuel wasn’t anything as fancy as rocket candy, the lab-made, sugar-based fuel that he’s previously used in his rocket experiments. Potassium nitrate is just one small step... but in this new world, it’s still the first one that he’s taken on the path to up there.


	3. Up A Tree

**Summary for the Chapter:**

> A bit of exploration leads to some unpleasant thoughts, and an unexpected discovery.

**Notes for the Chapter:**

> At one point, before Taiju broke out, Senku did find Yuzuriha.
> 
> See end notes for additional content warnings.

One thing Senku that hasn’t done much, as of yet, is exploring. He’s hiked down the river to the sea shore and roamed the nearby woods, but that’s about it. He’s been busy with more localized concers. Now he has more time on his hands because he can finally store food for more than a day or two without having to carry it with him or worry about spoilage and hungry animals.

Using this new freedom to get a better idea of the lay of the land sounds like a good idea. The more he knows about his surroundings, the more potential sources for food and materials he has access to. If he’s astoundingly lucky, he might even find visible remnants of a particularly big building and secure himself some iron oxide in the form of rusted-out remnants of steel. That's probably not going to happen, but it’s still worth keeping an eye out for.

Navigating in this environment is complicated by the fact that he has no idea how much the landscape has shifted over the millennia. There’s been some sort of a flood at some point: he’s clearly been moved around while he was unaware of his surroundings, and that hints at the river maybe not having always been where it is now is. There sure as hell wasn’t one near the school, but then rivers do shift around a lot, when you look at them over a timespan longer than a few years.

The flooding could have happened when the dam of the local reservoir lake broke, or because of a typhoon or a tsunami. Whichever is the case, he’s lucky that he’s still in one piece. Not everyone he has seen has been as fortunate: many of the stone people who litter the landscape near the river are missing pieces. Looking at them quickly got unnerving enough that he decided to set himself up further up in the woods just to avoid constantly tripping over them. They might be stone all the way through, but seeing people-shaped lumps with their hands or legs snapped off, or with half of their head missing, wasn't really the sort of thing that helped you start your day on a high note.

The people do, however, give him a clue. The way they’re clustered near the river suggests that the waters that moved them came from upstream rather than from the sea. The same flood that left them there must have moved Senku, too, because he hadn’t been too far from the river, either.

He spends the better part of an afternoon wandering up and down the stream, examining the stone people he finds there. On closer inspection, they appear to be cracked or shattered instead of being weathered or worn. Looks like whatever happened to everyone has conveniently also made them remarkably resistant to erosion.

If he follows the river upstream, he should be able to find the remnants of the dam, even if he finds nothing else. There’s a chance he can use it to get some idea of what had been where in the surrounding area. He would need to stick close to the river, because finding his way back could prove difficult if he doesn't. A compass would be incredibly useful, but until he can find some magnetic ore, he will have to make do.

-

The next morning, Senku packs some supplies into a couple of bags that he ties to his waist. Once the dew on the grass has evaporated, he sets out.

Even if he follows the river, it pays to look for things he can recognise later as he ventures further. It's easier said than done, because everything has changed. There are precious few larger landmarks left, and the few that are there are not the sort of thing he had on his mental map of his home town. He knew where all the hardware and IT stores were, and he could have navigated the streets between the school and his home with his eyes closed, but he hadn’t had a clue that there was a cave in the area. It might have appeared later, but that’s not very likely, considering how slowly non-volcanic cave formation generally happens. Chances are it was already there and he just didn’t know about it, because he had tended to avoid rubbing elbows with nature directly, save for the few times he needed a secluded launching place because dad hadn't been able to secure a permit for him. 

Which brings him to another complication: he’s _really_ not used to finding his way around in this kind of a landscape. To his eye, everything is just green, trees and shrubs, more trees and more shrubs, and more green, with the occasional dash of rock here and there. All of the trees and all of the rocks look the same. If this was a MMORPG, he would complain about bad design. He sticks to the river like glue, because it's the one thing he can reliably use to get his bearings: if he doesn’t know where he is, he will at least knows which way to go.

He will eventually need to venture further out, because the river basin and seashore will only yield a limited set of materials for him to work with. Once he does, he will need something to help him get his bearings even without familiar landmarks. A sextant would be great, since he has nothing to make mirrors with, he’ll have to make do with something more like a a backstaff.

His eye catches on a plump person with one arm pillowed awkwardly over their head. It looks like they had been sleeping when they were turned into stone, and then got flipped over at some point, so that what used to be down for them is now up. Maybe he can use the people as signposts? They stand out to him from the landscape in a way that the trees and the rocks don’t.

He presses on. The dam will be a good goal for a later date, but he thought it over and decided that the first thing he does in this navigation venture should be to see whether he can find the place where his school had been. It’s where he had been when this whole thing happened, and it’s where the flood – or the first flood, if there’s been several – picked him up and carried him away. There’s no telling how far he might have been carried, but he must have ended up at least five kilometres downstream, because that cave couldn’t have been anywhere near the school. 

He had been indoors and on the third floor, both of which are factors that would have affected how far the flood took him. There’s no chance of calculating something like that, because turbulence is far too complex for the human brain to handle, and there are so many variables involved here that it would make even a supercomputer stutter. One of the few things he _can_ reasonably deduce is that the people in his vicinity would have stood a greater chance of washing up near him than the people who had been further away. If he wants to find a specific person – say, someone from school – he’s going to have to create a fan-shaped search grid. For that, he will need a starting point, and to have a starting point, he needs to locate the school grounds.

He rounds a bend in the river and pushes some branches out of the way, and then he revises his opinion about using the plantlife as landmarks, because right in front of him stands probably the biggest tree he has ever seen. It's massive enough that it breaks above the surrounding canopy and leaves space for sunlight to finds its way in all the way to the ground.

When he gets closer, he notices a reddish colour to the young leaves clustered at the ends of the branches. The rest of the leaves are a glossy, vivid green, and the branches spread out in a distinct shape. So it’s a camphor tree. Wasn’t there one at the school yard? If this is the same one, it’s far older now than even the really ancient one that grew at the Temples of Kinomiya had been. Trees can live to incredible ages when compared to animals, but he’s still not sure one could survive for 3,700 years. Nearly four millennia is a very long time, even for a tree: there’s only been three confirmed and six unproven cases of a tree trunk that has reached anything close to such an age.

No one’s interfered with these trees in millennia, though, so who knows how how old some of them might be. This trunk could also be a clonal specimen that grew from the same roots as the original tree. Trees do that. Camphor trees also aren’t that common at this latitude, and they weren’t that common in his home town, either, yet looking around, he spots several more of them, though none is as big as the one in the middle. It could mean that he’s close to the school yard used to be, because when he looks around, he appears to be standing in a patch of forest made largely out of camphor trees.

If this is the right place, there’s nothing visible left of the school buildings. He expected it, because so far he’s seen no remains of any buildings, but the possibility still unsettles him. It _has_ been close to four thousand years, and that it stands to reason that nothing much would be left, but it’s still really weird and kind of freaky to look at this place and try to project his mental map of the school onto of it.

Would he be able to find the place where his home had been?

A memory pops up, of pushing the front door open, backpack weighing on his shoulders, and seeing rice balls and sauce set out at the table. A wrinkled face, framed with grey hair tied up in a loose bun, turning to smile at him.

_Gran_.

He’s almost overcome with the sudden urge to start running. He doesn’t, because he only has the vaguest idea of which way to even go, let alone how far. If he gives in to the impulse, he would just end up getting lost like an idiot, and he can’t afford that.

Besides, even if he could somehow find home, Gran wouldn’t be there. She popped back to her hometown for a couple of days—three thousand, seven hundred and nineteen years ago, when it took three and half hours to get there by train.

Get it together, Senku. She’ll be fine where she is. Concentrate on one thing at a time. He closes his eyes and breathes shakily. In and out. In through the nose, out through the mouth, and slower on the exhale. After a while, his heart rate starts to level out.

Once he feels a little better, he decides that his next course of action should be to check out the camphor copse for any signs of long-gone buildings. It might turn out to be pointless, but this is his best clue so far, and he gains nothing from overlooking potential evidence.

If there is any, however, it's buried under a layer of topsoil and obstructed from view. He has neither the time nor the tools to start doing actual archaeological excavations. For now, the conclusion has to be that if the buildings were here, they're completely gone now, just like every other building in town.

He’s actually _very_ lucky, because if he hadn't been washed out of the the building, it might have crumbled on him and crushed him, or buried him deep enough that being revived would have meant an immediate and gruesome end. Having wandered into the hallway to eavesdrop on his friends might have ended up saving his life.

It's not a pleasant thought. He should think about something else. He should take a couple of camphor branches with him; he can use those to repel insects. More resources is good. The biggest trunk is the closest one, so he might as well get them from this one, even though he’ll have to climb a little.

The base is covered in shrubs and vines. He clambers over them and uses his chert knife to hack away some of the growth in his way. It’s thick and viny, and he gropes around in it to find a secure handhold. His hand lands on stone. What is that doing up here in the tree?

Could it be...?

No, _surely_ not.

He cuts and tears at the vegetation with sudden vigour, exposing more and more stone, until finally he can see enough of the hidden person to be sure. He sits rather abruptly down on the massive root under his feet, feeling a little nerveless, and stares at the dark grey contours of a familiar face.

”Hello, Yuzuriha. Fancy seeing you still here.”

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- Speculation on a few ways in which Senku's adventure could have ended before it really had a chance to begin  
> \- Description of homesickness, a sense of alienation, and a short, fleeting panic attack


	4. Nothing's Exciting Enough to Stay Exciting Forever

**Summary for the Chapter:**

> At some point, the novelty was bound to start wearing off, and the drudgery would inevitably set it.

Three days after he finds his friend in a tree, Senku opens his eyes in the morning and doesn’t want to get up. He does do so, and he goes about the rest of his day like he has before, but the feeling is jarring enough to stand out.

Two days later he lies down to sleep and his back starts to hurt. Stretching makes it stop, but it comes back twice. He finally drifts off, late into the night, and the pain is gone when he wakes. He still hesitates to lift heavy loads for a while.

A week later, he nods off while he’s tending to a cooking fire. His dinner burns and he has to go to bed on an empty stomach. It reminds him that he needs to start thinking about stocking up for winter.

Over the next few days, he concentrates on building up food reserves and brings in several large baskets’ worth of forage. After he hauls in one particularly heavy batch of mushrooms, his brain suddenly tells him that _that’s it,_ and makes him fall onto back. The sky above him spins in lazy circles. When he brings his hand up, his fingers spin with it. It makes him feel dizzy enough that he squeezes his eyes shut.

He’s reached a point where he can no longer push himself like this without risking long-term consequences.

It’s aggravating. Even though he’s worked his ass off, he's still barely able to do anything more than look after himself. He’s never going to get anywhere at this rate. It took him months to get this far, and he hasn’t really even made it past the starting line. How the hell are you supposed to build a civilization when you end up feeling like you might puke from sheer exhaustion because you're trying to make sure that you don't starve in the winter?

His brain has no answers to give him. It has also had it up to here with talking to itself.

-

”... so you see, if I could wire up sensors tuned to specific wavelengths of light, not only might I be able to rig up a somewhat accurate measure of time, but I would also get a handy light-triggered alarm clock out of the deal. Once I have electricity, that is. Not that alarm clocks are exactly a priority here. It’s just odd to think that we were so used to knowing exactly what time it was, at all times, and now the closest I can get to that is counting seconds after sunrise, assuming I wake up in time to see that happen.”

Yuzuriha looks past her raised hand and out into the camphor tree copse. Or she would, if she could see anything. She can’t, because she’s still stone, and Senku knows from personal experience that you don’t get sensory feedback in there.

It also means that she hasn’t heard a word he has said. That’s all right, though; he hasn’t really talked about anything important, even if he’s already been here for half an hour.

He’s here because aide from being tired, keeping a fun log in his own head also isn’t really cutting it any more. For all practical purposes, Yuzuriha is a lump of rock, but talking to her is still somehow different from talking to himself – or to an actual lump of rock. This lump of rock that’s shaped like his friend at least holds the potential to revert back into her.

”When did you grow all that chest, by they way? I don’t think those were there the last time I saw you without a shirt on.” He leans back against the tree root and looks up at the canopy. Patches of blue sky peek down at him through the foliage. ”Did I ever tell you I used to be scared of boobs? And I don’t mean ’nervous about’ like Taiju used to be in fifth grade, I mean absolutely screaming terrified. Dad’s never admitted anything, but I bet that was a fun ride for everyone involved.” He glances at her. ”I got over it, don’t worry. These days I don’t really mind them, as long as they’re attached to someone other than me.”

Something rustles in the bushes on the far side of the river. Senku watches them until he sees two squirrels run up a tree, chasing each other.

”Speaking of things being attached to you, once you’re all flesh again, _do not_ sit down just anywhere, especially for long periods of time. I promise you that you _will_ regret it if you do. I’m probably asking for trouble by having been here this long. I miss park benches. Man, I miss parks being a thing you could _leave_. I almost missed being stone, for like five minutes after I stood up and realised for the first time the gravity of the mistake I had made by sitting down for too long. It’s a hard-earned lesson that I’ll gladly pass on to anyone who listens, along with some complimentary salt.”

The squirrels make angry, tsk-ing noises at each other. One of them leaps for the next tree, misses, and lands in a bush. It scrambles up into another tree, apparently unharmed.

”The work I’ve been doing is hard. It’s not really difficult to do, but it’s the kind that takes a lot of time and effort. And it’s constant. I can’t take long breaks unless I also want to stop eating.”

It’s a bit sad to be rattling off your woes to a petrified, unresponsive statue version of your friend, but he feels better for doing so. It’s been a long while since he got to talk to another human being.

”I don’t really have a problem with working a lot, but it takes more strength than I would have imagined. Muscle power is not really one of my strong suits, like you know. I had Taiju around for that, and before him, it was dad who carried the heavy bags. I hauled in two baskets of forage yesterday, and it took me the whole afternoon. I bet Taiju could have done it in one and a half hours.”

Would it be better if she could still see or hear something, even if she couldn’t speak or move? It didn't sound like it would be great. How did it work that while he was still trapped in the stone, he hadn’t been aware of any kind of sense-related feedback, but he could still think? What _is_ this petrification like? What are its defining characteristics? Does it resemble anything else that he knows about? Is it like cryptobiosis?

Tardigrades, tiny six-legged bear-like things that live in mosses all around the world, do that. They can stop almost all of their cell functions and could even survive the vacuum of space in that state. Drop them in a dish of water afterwards and most of them would be fine, at least until radiation damage caught up to them. Does this petrification somehow resemble that?

When tardigrades go into cryptobiosis, they spit out 99% of the water in their bodies. They don’t change phase when they do that; they change volume and shape. Humans don’t come equipped with that ability, and if it was done to them by an outside force, he imagines they wouldn’t rehydrate very well.

”I don’t think you’re in cryptobiosis,” he tells Yuzuriha. ”You don’t look anywhere near shrivelled enough for that to be the case.”

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- creeping signs of overexertion, exhaustion and loneliness


	5. I'd Rather Sleep In, If It's All the Same to You

**Summary for the Chapter:**

> He can no longer put this off. He needs help.

Talking to Yuzuriha becomes part of his routine. He goes for long stretches without necessarily even thinking about her, but then the lack of company starts to weigh on him and he turns his foraging trips in the direction of the camphor copse.

”Hey, remember that movie we watched about the guy who got shipwrecked onto that uninhabited island, found a ball and drew a face on it so he’d have someone to talk to, and then it became his best friend?”

It had been a movie night at Taiju’s place, with an old flick called _Castaway_ that Taiju had found at the library and wanted to see. He had gotten so emotional over the film that he cried into the popcorn and ruined it. Senku remembers being annoyed about the whole thing.

”I know I said that _The Martian_ was a much better take on the same theme, and I still think that, but I'm kind of starting to understand that guy and his ball a little.” He chuckles. ”I promise not to draw on you. There's no need to give you a face because you already have one, and if I absolutely have to draw on something, I’ll do it on Taiju. He's got a better mug for it, and he's my buddy and my brother, so that kind of thing comes with the territory. Though if he ever did something like that to me, I'd kill him.”

There’s no wind today. The squirrels seem to have moved on. Silence hangs over the camphor tree copse. Yuzuriha, predictably, doesn't break it.

Senku glances up at her. ”I don’t really know why I’m talking about this.”

Yuzuriha's stone face looks very lifelike. He frowns, pushes himself to his feet and examines her up close. She has been exposed to the elements for over 3,700 years, yet she still has eyelashes, and even what looks like a half-developed pimple under her ear.

The details on the petrified people are incredibly well-preserved. He hasn’t really paid that much attention to it, beyond absent-mindedly making a mental note on it, but now it rises out in stark relief.

It’s been almost four millennia. Rock carvings tend to lose their fine detail over time unless they’re buried or otherwise preserved in favourable conditions. Many of the petrified people are fully exposed to the weather, and probably have been for all this time, yet most of the damage to them seems to have come from cracking, not from erosion. There’s something up with that.

-

A few days later, Senku wakes up already tired.

He groans like an old man when he raises his arms to rub at his eyes and squints at the door in irritation. The light is too bright, and his muscles ache from overuse.

It’s not the first such morning. It’s one among several, and they have been coming with increasing frequency.

He doesn’t want to get up. He wants to turn over and go back to sleep.

Instead, he makes himself crawl out of bed, shimmy down to ground level, and start a fire. He considers his vegetable mush solemnly while it cooks. 

He can no longer put this off. He needs help.

-

He _has_ been putting it off, hasn’t he?

It’s a question Senku asks himself an hour later, as he sorts out the contents of his cooking fire pit. He has two of them that he alternates between, switching every couple of days. Once one has cooled thoroughly, he puts the coal in a basket and the ashes in a pot, and stores them under his house until he has a use for them. If it has rained heavily, he throws the ashes away, because much of the useful stuff will already have leached out.

Establishing basic survival necessities for himself has obviously been his first priority here – as it should – but seeing how he’s already made salt and potassium nitrate, he can’t honestly say that he’s still at that stage. He _has_ been working hard, but not all of that work has gone into immediately securing himself, and it’s been that way for a while now. His food system is still firmly at the gathering stage, but he hasn’t been living quite as much hand-to-mouth as one might think. With his handy preservatives, he’s pretty set for the coming cold season, and his calculations suggest that he doesn’t actually have to haul in heaps of food every day to make it through the winter. What he already has should last him over two months, and there's plenty of time left. So what’s the deal here?

He can think about that later. Since it’s clear that he does, in fact, have the resources to start looking into getting the help that he needs, he now has a new goal to focus on. The process that leads up to that goal can be broken up into three discrete steps:

Step one: choose a candidate  
Step two: figure out depetrification  
Step three: depetrify the candidate

It sounds simple, as long as you couch step two between steps one and three and don’t look too closely at the details. 


	6. Sure Could Use a Hand Here

**Summary for the Chapter:**

> You can’t really tell much about someone just by looking at one of their limbs.

**Notes for the Chapter:**

> See end notes for additional content warnings.

When choosing someone to help him restore humanity, Senku could, rationally speaking, pick any suitable-looking musclehead that he finds lying around in the underbrush. None of them is more familiar to him than any other, and there’s a high likelihood that whomever he picks will quickly become ten billion percent invested in helping him once they're out of the stone. It’s the only reasonable course of action available to them, after all.

He stops to consider one person who looks big and strong and intact. If he had to guess, he’d say that this one is a cis man in his thirties.

The expression on his face looks unfriendly. A tiny dark hole opens up at the bottom of Senku’s gut.

This guy looks like he could easily do all the heavy lifting that Senku needs someone to deal with, but he also looks like the sort of person who likes to get drunk with his guy friends and travel around the town in packs, forcing other people to get out of the way or risk the consequences. He looks like the kind of a person that his friends in his peer support group sometimes talked about, sharp words not quite hiding the fear in their eyes.

Well, that explains that, then. Who _wouldn’t_ try to get by on their own, for as long as they could, if getting someone to help you meant risking that someone becoming a problem? 

Most people are reliable, decent and reasonably thoughtful. That being said, how much you can _really_ trust someone is a far more pressing question in these circumstances than it was in the old world. When there are a lot of people around, it raises your chances of finding friends and reliable allies, and peer pressure keeps people in check. Humans are a social species, and for the most part, they work well together. The fewer people there are, however, the more pronounced the question of someone’s trustworthiness becomes. The last thing he needs right now is some entitled, sexist and potentially violent moron who would take issue with him being trans. He’ll have to deal with people like that again eventually, of course, but right now it's his choice, and he’d love to postpone that for as long as he can.

He needs manpower. Cis-looking men are his best bet for that. He also needs to look out for his own well-being and to find someone he can work with so that he can keep taking the steps to restore the civilization without undue interference. That’s necessary. People who look like they aren’t cis men are his best bet for that. The problem is that he can’t really forgo either of those things, because each of them is necessary but not sufficient on its own. Unless he stumbles over a really big and strong person who’s ten billion percent obviously not a cis man, he’ll have to find a way to strike some sort of a balance.

-

”I could pick you, of course,” he tells Yuzuriha the next time he visits the camphor copse. ”But you’re hardly much stronger than I am, so there's a distinctly non-zero chance that I wouldn’t be doing either of us a favour by depetrifying you this soon. You’re all about crafts, not muscle power. Besides, I’d like to at least have something for you to work with once you’re out, like those plant fibres your crafts friends told me about back when we were dyeing yarn.”

-

There’s a hand sticking out of the ground near the cave where he broke out. It’s close to the path he takes when he goes there to pick up bat guano and court deadly disease, so he sees it often enough.

You can’t really tell much about someone just by looking at one of their limbs. The distance from the cave to his tree house is impractical for any kind of experimentation. So is going to the effort to dig someone out, since there’s already plenty of non-buried people available all over the place. And for all he knows, it might be just the limb, with no body attached. All he does really know tell is that since it’s near where he was, it probably came from the same direction as he did. Still, whenever he sees that hand, he gets this feeling. It lingers with him even after he's returned to the tree house.

Intuition isn’t always a good basis for decision-making, but Senku has never been under the illusion that he is one hundred percent rational.

Next time he goes, he takes the shovel with him.

It turns out that the feeling _was_ telling him something. There is an entire body under there, and once he brushes the dirt off its face and reveals its features, Senku sucks in air so abruptly that his lungs twinge. He straightens, slings the shovel onto his shoulder and takes a moment look at the guy he has just unearthed.

That hand was sticking out of the ground because he is holding both of his arms out in front of him. He has that stubborn look on his face, the one that Senku is very, very familiar with, and his open mouth is full of dirt. He was probably yelling at the green light when he got hit.

3,700 years have passed and people have been scattered all over the place, yet somehow Senku has found the one face that he has already seen more of than he ever wanted to.

”Hello, big oaf.”

Step one is complete.

Now it’s on to step two: the Senku Laboratory for Depetrification Research.

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- Trans man briefly contemplates the danger unfamiliar cis men might pose him


	7. A Major in Depetrification Studies

**Summary for the Chapter:**

> This could lead to a whole new branch of science. Perhaps even previously undiscovered natural laws. And it's right there, waiting for him. History books, here comes Senku Ishigami: the self-taught scientist who restored humanity, rebuilt civilization and established a brand new scientific discipline while he was at it. Oh, and by the way – he’s sixteen and he’s trans. Isn't that exciting?

The most logical way to start thinking about how to undo the petrification is to ask what caused it in the first place. The first hypotheses he comes up with for that sound downright silly, but the petrification itself is such a ridiculously implausible phenomenon that it seems careless to discount even things that are really out there, like the sort of super weapons that normally populate super hero stories.

Or an alien attack. In a debate about extraterrestrial life, he would be among the first to claim that it's a statistical inevitability, but if aliens are behind this, it's really not the kind of first contact situation that he would have hoped for. The Star Trek model would be much better that the Pacific Rim model, even if aliens are totally not going to look like humans with green skin or extra bits on their heads. 

It could be a virus? A magic virus carried by what appeared to be light. Yeah, right. He's probably been thinking too much about bat pathogens because he's spent so much time in the cave.

All the really knows about the petrification phenomenon is that it’s species-specific, that it affected swallows during the first wave and humans during the second, and that it has affected nothing else that he's been able to determine. It honestly sounds like some kind of an insane fantasy.

Insane fantasy or not, there must be an underlying rule to how it works. Whether it's simple of complex, everything in the universe operates on some kind of a set of rules. All his studies on science have prepared him to figure those out. And once he knows those rules, he can fight this – even if it’s like nothing anyone has ever seen before.

This could lead to a whole new branch of science. Perhaps even previously undiscovered natural laws. And it's right there, waiting for him. History books, here comes Senku Ishigami: the self-taught scientist who restored humanity, rebuilt civilization and established a brand new scientific discipline while he was at it. Oh, and by the way – he’s sixteen and he’s trans. Isn't _that_ exciting?

-

He spends the day in frenzied thought, observation and testing, and what he gleans from all that is as follows:

Fact one: When the petrification is undone, the most damaged parts of the outer layer are shed as a stone shell, while everything else turns back into living tissue. That probably means he shrank a little. This is not exciting. He determines that his lost centimetres add up to less than one and a half by checking the stone shell that he shed when he broke out, so at least it's not _that_ much.

It’s not _really_ a concern, but he’s a bit miffed about it, because his growth spurt got delayed by the puberty blockers and that left him a little on the short side to begin with. At least it will happen to everyone, so he'll still be the same size relative to other people.

The _real_ issue here is that he’s been using his finger joints as a quick, rough measuring stick, though given that the shrinkage is around 0,8 % and he’s likely grown a little in the past months, that should be fine for a while. Long term, he ought find some way to give himself standard measurements to keep track of things, anyway. Centimetres are enough of a pain to not be worth it right now, but maybe he can do something with the degrees he’s started to carve into his bargain bin sextant.

Fact two: The depetrification was triggered by an outside factor. There's not much to add to this, but it is, hands down, the most exciting part, so it deserves a separate item on his facts list.

Fact three: That outside factor probably involves the nitric acid he discovered in the bat cave. This is both exciting and frustrating, because the nitric acid either broke _his_ petrification, specifically, or breaks leftover petrification on someone who has _already_ been depetrified, or requires long exposure to work. Whichever the case, a single dose doesn't appear to be enough on its own. Dumping nitric acid on a petrified Taiju didn’t do much. Dumping it on other petrified people to double-check didn’t do much, either.

It’s probably just as well that he didn't work it out right away, because he got so worked up about it that he forgot to clean out Taiju’s mouth thoroughly before he dumped the nitric acid on him and leaned in really close to watch. Had Taiju actually been depetrified, Senku would have gotten his face sprayed with spit and dirt.

He walks back to the tree house as the sun is setting, mind still whirring. He has his candidate now, one that checks positive on all his requirements. He has some ideas. Now he needs to throw all his loose resources at this and figure it out. He can start by picking up more of those stone swallows that he’s seen lying around here and there. They can serve as his first line of test subjects.

And he needs an actual laboratory. Every self-respecting scientist should have a laboratory.


	8. Probably Not the Same Thing That Happened to Dinosaurs

**Summary for the Chapter:**

> On the agenda: chop wood, haul rocks and extrapolate wildly on the chemical properties of an unknown substance.

For the next three days, Senku chops wood and hauls rocks. His arm and back muscles must have grown, because they don't die on him quite as much as the last time. Though he does get somewhat achy and sleeps through the night like the dead.

Bit by bit, the walls of his brand-spanking new lab go up. By the time he moves on to attaching the roof, his eagerness to have it done finally wanes a little and he wanders back to the cave.

Taiju is right where Senku left him, lying in a pit with his arms sticking out. His eyebrows are doing that thing they do when he gets really serious, and that look is now permanently frozen on his stone face. When Senku leans in closer, he can even make out some outlines of individual brow hairs.

It's the same thing he saw on Yuzuriha. The same thing, in fact, that he's been seeing over and over on every single petrified person he has examined, up to and including the swallows. Some of them have cracked, but on all of them, signs of erosion are minimal.

”How are you still in such good condition?” he asks Taiju and taps him on the temple. ”I know you’re exceptionally hard-headed, but I don’t think that’s causing it, since it's affecting everyone else, too.”

He pokes at several other petrified people and peers intently at the imperfections on their surface, close enough that his nose almost touches them. They all look like they’re carved from stone, and the stone looks the same on all of them. Even when he specifically looks for it, he finds no exceptions that stand out.

By comparison, the bits that fell off him when he broke out are more brittle. Their edges have already started to lose their sharp definition, and he’s even able to snap one in two with his hands. When he does so, small grains fall off from the fracture site. Does the material require the rest of his body to keep its integrity, or is whatever broke him out still working on these bits, breaking their down composition? They’ve turned kind of crumbly, but they still look like stone.

Is he looking at some sort of mineralization here? What minerals would the petrification process utilise, if it does? His senses tell him that he’s looking at some type of a rock, but of course he doesn’t know for sure that's what it is, chemically speaking. Mineralization just seems like as good a place to start, and in any case, it’ll probably take longer to rule out than cryptobiosis.

There are some examples of highly detailed fossilization that he's seen in pictures, like that frankly amazing nodosaur fossil that was unearthed in an oil sand mine in 2011. It looked almost exactly like the actual animal would have looked when it lived, but the fossil had still taken ages to form, and all those soft tissues had only been preserved in such perfect detail because the dinosaur got buried under a ton of mud immediately after it died. In contrast, the petrification happened so fast that actual mineral replacement is extremely unlikely.

It's doubly unlikely because unlike fossilization, the petrification can actually be reversed. That suggests that whatever substance solidified into rock must have been in the bodies themselves, or at most in their immediate environment – in other words, in the air. Though compared to solid matter, air has such a low molecular density that it wouldn't be able to supply much mass. That means that the elements that were already in the bodies are his primary candidates, especially the ones that occur a lot in minerals – solids with a crystal structure - and mineraloids – solids without one. He can go through those, one by one, if he needs to.

Calcium is the fifth most abundant element in the human body, after oxygen, carbon, hydrogen and nitrogen. Besides carbon, which involves its own branch of chemistry, calcium is the only one of those that isn’t a gas. Could its reactions with the other elements in the body be involved in the petrification?

Calcium plus oxygen makes calcium oxide, which turns mortar-like if you add water, so that's a nope. What about nitrogen compounds? Calcium nitride and calcium nitrate aren’t exactly known for their durability, so probably not those, either.

The carbon and the calcium could have formed calcium carbonate. That’s even a type of naturally occurring stone: marble. Could that be it? Well, not really. Calcium carbonate inevitably wears down from exposure to weather. The petrified people have been belted with the acidic rain caused by atmospheric pollution, and later, after that cleared out, with the carbonic acid that comes from the carbon dioxide that always dissolves into rain water from the atmosphere. Calcium carbonate would have broken down way worse than this under four thousand years of that kind of an onslaught.

Besides, the 1,4% of calcium in a human body would be nowhere near enough to solidify the rest of it, even with the help of the carbon. His 56 kilos of body mass could be turned into just under two kilograms of calcium carbonate. Not to mention that most of the calcium is already bound into the bones and the teeth. How would it spread out and then compress back in? So that's two strikes against that one, too. Calcium carbonate, you’re out.

Though he'll let it back in later, because it's a very useful mineral.

**Notes for the Chapter:**

> Writing this guy is an Experience. I have googled So Much, drawn a bunch of actual chemistry process charts, and even gone so far as to check out chemistry books from the library in an attempt to understand what he's doing and what he might be thinking. It may not have been strictly speaking necessary for story-telling reasons, and it often makes my head ache, but I then look at this little science vegetable again and think, ”challenge accepted”.


	9. You Can Take the Boy Away from Science, But You Can't Take the Science Out of the Boy

**Summary for the Chapter:**

> This whole thing has shot clean out of the orbit of all things known to humankind and hurtled past the Neptune of Outlandish Theories into the Kuiper belt of What the Actual Fuck. Or, In which Senku demonstrates that he is, indeed, the nerd character.

”So what's your take on this whole thing?” Senku settles himself comfortably onto the massive root. So far he hasn't run into a single leech here. Maybe they dislike camphor trees. ”That’s a rhetorical question, by the way. I don't expect you to give me anything, because you can’t hear me and you can’t speak. But if you had to, what would you guess the petrification phenomenon is? You never know; what you think might actually turn out to be useful. Sometimes clueless amateurs land on answers that specialists have missed, because they’re better at thinking outside of the box.”

The squirrels are back. Their rowdiness doesn't look like mating behaviour. Besides, don't most animals mate in the spring? Maybe there’s a nest nearby and these are this year's offspring, messing around aimlessly because they’re basically just kids and their parents still feed them? They look like they don't have a care in the world.

Getting envious of squirrels is not on his list of things to do for the day.

”I'm starting to think that calcium is a dead end, at least as far as it comes to relatively simple compounds. Maybe it’s some kind of a carbonization instead. Carbon makes up 18 percent of the body, and it does form a lot of different compounds with oxygen, hydrogen and nitrogen. I think I'll look into that next. Good chat. Thanks, Yuzuriha.”

-

If the petrification had turned the elements in the body into simple oxocarbons, hydrocarbons or carbon nitrides, those would have just evaporated or leaked away. More complex ones, one the other hand, would stay in place and form a stable structure.

Whatever chemical composition the petrification creates, it has to be really durable. Perhaps sort of a crystalline structure is involved? Could the carbon have turned into a sort of opaque, ugly version of diamond? It could Or, say, something like heterodiamond, a type of superhard material you get when you basically contaminate diamond with cubic boron nitride by blowing the shit out of them.

Heh. There's a bad joke in there, just waiting to be picked up.

Leaving aside carbon's square derivates, there’s also carbon nitrides, which inclune a predicted superhard material called beta carbon nitride. It's supposed to be even harder than diamond. No one’s actually been able to manufacture that yet, but being able to make theoretical materials doesn't sound impossible for something that can actually turn people into stone.

He pointedly ignores the possibility of elemental transmutation for now. There’s no way to analyse petrified tissue to determine whether the elements themselves have actually changed, rather than having been reorganised into different compounds. No matter how strange the petrification phenomenon is, and no matter how much respect he has for the early alchemists for laying out the groundwork for chemistry, he’s not going to resurrect thoroughly debunked concepts unless no other hypothesis pans out.

Besides, for the petrification to involve actual transmutation of the body's most abundant elements into heavier ones, you would need a fusion reaction that could be sustained outside a star core or a fusion chamber. The reaction would have to have been caused by that light, like a beam-target fusion would be, and it would also need to have worked precisely at a macroscopic scale, which no known system of beam-target fusion could do. And even if you somehow achieved all that, you would still have to make sure that it affected only a single species of animal when you exposed the entire environment to it. The idea is even more out there than an alien attack.

Not that this whole thing hasn't already shot clean out of the orbit of all things known to humankind and hurtled past the Neptune of Outlandish Theories into the Kuiper belt of What the Actual Fuck.

Even so, he is not going to bow down and hand this over to the realm of science fiction. Even if the petrification turns out to be a textbook case of Clarke's Third Law – a type of technology advanced enough to be virtually indistinguishable from magic – it will still operate on a set of rules, and those rules can be found and exploited.

-

If you take out three gases and the carbon, there’s less than five percent total of other elements in the mass of a human body. Even adding carbon back in only brings that number up to 22%. That still isn't much, and it suggests that either the gaseous elements are also involved, or that there's some sort of an anomalous crystalline restructuring going on.

Perhaps it's a lattice? A _really hard_ lattice.

The diamond and beta carbon nitride that he has already considered achieve their exceptional hardness not because of the elements in them, but because of how they’re organised at the atomic level. A lattice made of carbon or carbon nitride could potentially utilize only a fraction of total mass to create a reiterating crystalline structure around the rest of the atoms in the body.

If there's a lattice involved, it would have to avoid messing with other chemical structures. The petrification process does that somehow – or at the very least, it retains the information on how to reconstruct everything when it's undone. If it didn't, depetrification would just result in an unpleasant glob of goo, or a pile of carbon with a pinch of other elements thrown in for taste. He already knows this is fortunately not the case.

The fact that he was able to maintain consciousness after being petrified means that cellular structures have to be preserved. His nerve cells were able to signal to each other, and for those signals to be able to run, the cells themselves have to be there. How that's possible he has no idea, but it's the conclusion he arrives at, anyway.

”You got any nerve cells zapping in there, buddy?” he asks Taiju and pokes his head. ”You got nerve in there, huh, big oaf? You got some nerve?”

Then he puts a hand over his eyes and grimaces. Four months of being stuck in a stone age forest on your own is no excuse to start sounding like a cheap beer commercial aimed at men who are insecure in their masculinity. If he doesn't nip this in the bud, next thing he might find himself making manly deodorant – which is pointless – trying to eat raw meat – which is impossible for human teeth to do and a health hazard besides – or hanging off tree branches, pretending to be an action hero hanging off a helicopter – which does not even merit comment.

Besides, he's always been more of the nerd character type, anyway.

**Notes for the Chapter:**

> I bet that Senku could shore up some crackin' science jokes.


	10. Don't Run Windows On That, It Might Crash

**Summary for the Chapter:**

> In which Senku continues to be a nerd, albeit this time a slightly more morbid one.

Not all of the exploratory things he does revolve around the petrification. On this particular afternoon, he's trying to figure out how to roast acorns without cracking them open to kill any grubs that might be in there, and also without setting said acorns on fire in the process. He does not have it down to pat, and he's not entirely convinced it's even a good idea, but you never know what works unless you try. That’s how you learn and change.

Besides, he's already spent the morning picking up all the petrified swallows he could find, and he can use a change of pace.

Speaking of changing and learning, one would think that spending 3,700 years trapped inside your own head would change your brain more than it did to him. When you stop to think about it, that should have changed his brain so much that he should actually be messed up beyond recognition. Yet he came out of the petrification more or less the same as he was when he went in.

Perhaps that means that when you're petrified, your nerve cells are somehow constrained? If the brain remains operational, but there is a crystal lattice present that somehow prevents major changes to its structure, it would explain why he didn’t emerge as a gibbering, incoherent wreck who could no longer make sense of light or sound waves, and who would have died within minutes from lack of heartbeat and breath. Spending 3,700 years without having to breathe once and then immediately remembering how to do it when you needed to sounds pretty implausible.

If his brain had adapted in response to the changes brought on by the petrification, brain regions responsible for sensory processing and organ functions should have long ago been appropriated for something else. Brains are plastic; they change according to how they’re used, and if you don’t use something you lose it, because it’s metabolically costly to keep stuff that you don't use. Yet it doesn't seem like he even got all that much better at counting.

This means that either those brain regions somehow retained all their functions without being used even once for nearly four millennia... or that the physical changes to his brain were curtailed in some way. The way he gasped for breath and felt dizzy right after breaking out may have been a psychological reaction, and it also tells him that the automatic functions had been maintained, but possibly not perfectly preserved. What if things had changed, but only a little?

One side of his acorns has become charred, while the other remains pristine. He gives up and scoops them into an empty pot. He’ll try something else tomorrow. He puts out his fire, cleans his teeth with a stick and stows a couple of embers into another pot along with some moss and tree bark. They'll make his morning easier if they survive the night. Then he climbs into the tree house and shakes out his blanket.

Maybe being conscious during petrification was like running an operating system from a USB stick? As in, you had access to all the processing power, all the features and gimmicks and all the programs you had installed, but your storage capacity was limited, and the moment you turned the power off, the RAM got wiped and you lost all the changes you had made.

That would explain why he'd had very few new ideas during that time. Now that he thinks about it, that’s a pretty glaring clue. 3,700 years is a long-ass time to go without think up anything new, even without any external stimuli.

If that's how it works, it means that staying conscious was good for much more than knowing when to wake up. If he had checked out at any point, his last memory could be from right before he was petrified.

It could also mean that over the centuries, he might have thought up a bunch of incredibly clever and useful stuff that he no longer has any inkling of. Because he didn’t realise he needed to keep them in mind, they would have been overwritten, probably by his constant counting.

It’s ironic, because the counting may not even have been all that useful in the end. He tried thousands of times to break out during a specific quarter of the year before he actually did, which honestly means that it was probably just a coincidence that it happened when it did. He had a 25% chance of breaking out during spring anyway. In the end, all that the constant counting left him with was the date.

There's something very uncomfortable about the idea of having accidentally erased your own memories. Your thoughts and feelings memories simply disappearing like they had never been there, not even being hazily retained as something just beyond your reach, is discomfiting as hell. What if some of it had been really important?

Well, there’s no point crying about it. What's done is done and what's gone is gone, and keeping track of time the only way he could was the best plan he had at the time. Besides, it may even have been useful. If he had had some sort of a mental breakdown or a dozen somewhere along the way, he may have restored himself from that simply by counting long enough to wipe it out, too.

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- A touch of existential horror related to memory loss


	11. Wouldn't Pay Ten Yen For A Copy of This

**Summary for the Chapter:**

> Note to self: next time you want to write something down, you idiot, get a lump of coal.

Think. Find a hypothesis. That's all he needs: one hypothesis for how to undo this thing.

Why is he different? Why does the nitric acid work on him, but not on anyone else? Think, Senku, think—

That's it! _Thinking!_ He never stopped doing it. That means he must have used 400 kilocalories a day, adding up to two terajoules in total over the time he was petrified. That's an awful lot of energy, but then, matter itself is just an awful lot of energy in another form. Thank you for that insight, Einstein.

The hypothesis looks like this: by staying concious, he consumed something in the stone. By consuming something in the stone, he weakened the petrification. By weakening the petrification, he made it possible for the nitric acid to break it.

It's rough around the edges, but elegant enough to put into a research article. He likes it.

-

He puts down the swallow he has been grinding with chert for the past fifteen minutes and wipes sweat off his forehead. The new factoid of the day is that petrified tissue sits above seven on the Mohs scale of hardness. He stretches his arms over his head and groans loudly.

Some of the monkeys that were poking at his failure of salted mushrooms on the side of the clearing start at that, but this time, none of them takes off. They'vegrown used to him.

The monkey's aren't bad company, and they're not even half bad conversationalists. For one, they never say anything criminally stupid – or if they do, he can't understand them. By now, they even understand him sometimes. They know what he meanswhen he says ”drop that” or ”get the fuck out of there”. Sometimes they even sass him back. Well, more like screech at him and throw sticks, but he gets the idea.

”You'd like these guys, Gran. I know you always had a soft spot for macaques, and these ones are even friendlier than the ones that lived in your home town.”

Then he blinks several times and looks around. Apart from the monkeys, he's alone in the clearing. There's no one else around.

He scoffs at himself and turns back to his task. ”Focus on what you're doing, will you?” Still, he can't help but feel like something in the air has shifted. It feels colder somehow.

-

He shoots up in bed in the dead of the night and bites off the strangled yell that woke him up. It still echoes in his ears. There was just one syllable, and although he only got two thirds of it out, he knows exactly what the entirety of it would have been.

 _Dad_.

He lies down and tries to go back to sleep. What else would he do?

What else _could_ he do?

 _One, two, three, four, five, six, seven, eight,_ _nine,_ _ten._

-

He has ground the swallows with every single mineral he has at hand. He has burned them in a wood fire, burned them with potassium nitrate, dunked them in river water, dunked them in sea water, dressed them in every possible combination of chemicals he has at his disposal, leftthem immersed in pots of filled with nitric acid, ot with nitric acid mixed with varying levels of other things, from everywhere between thirteen toseventeen days, and once, when he momentarily lost his grip on his composure, he has even shouted at them. And still, nothing.

It has been five months since he broke out of stone.

It has been five weeks since he started these experiments.

It has been five minutes since he was able to breathe normally.

In and out. In and out. In through the nose, slower on the exhale.

It will be all right. This just takes some perseverance.

-

What if he doesn't have the resources to figure this out? What if this is beyond his means? What if this is so far beyond all known scientific principles that there's nothing for him to grasp on to?

He can't give up. He will try everything. Whatever it is, he will try it. Try. Try, try, try. Try and try and try, and then _try some more fucking damn it try Senku TRY_.

And he must not forget. No matter how much this whole thing looks like a fantasy, the universe still revolves around natural laws. The foundations of science are unshakeable. Never forget. Never _ever_ forget.

_One, two, three, four—_

He needs to write this down. He needs to find something to write with and write this down somewhere where he can easily find it, so that if he overwrites his own mind, he won't forget, he must _not forget_ —

-

He crashes into bed late at night and winks out immediately.

-

Senku wakes before the sun is up because his thumb is throbbing.

His head hurts. When was the last time he drank water? There’s a jar of filtered water under the house. He drags himself up, climbs down and drinks three full cups. It doesn’t make him feel better.

He wants to go home. He wants to sit down with his laptop, skype his dad and watch him do a dumb trick with weightlessness. He wants to wake up in his own bed, eat heavily processed cereal for breakfast, try not to fall asleep in the literature class, havea shit ton of ramen for lunch, call his friend Miyuki to argue about chemistry, go to the lab to mess with his bottle cap stash and get annoyed when Taiju barges in to tell him that he _still_ hasn’t confessed to Yuzuriha. He wants to turn this civilization-building game off and put it away.

His feet know the path to the cave, even if his brain is somewhere else entirely. The rock wall looms into sight, and soon after that, so does the hole he’s shovelled into the ground.

The stone is cool and hard, but that doesn’t really matter because it’s still Taiju. Senku wedges himself between the edge of the pit and his petrified friend. Taiju has that same dumb, shouty expression he’s had ever since Senku dug him out. His arms are held out just the same, too. Senku looks at Taiju’s outstretched fingers. Then he reaches out and wraps his own fingers around them. Taiju’s hand is also cool and hard, and it's wrong, it's all wrong, but Senku holds on anyway.

”I don't know if I can do this.”

He didn't mean to say that. He didn't mean to say anything, but once the words start coming, it's hard to hold them back.

”This isn’t like I thought it would be. Even the simplest things take so much work. I can’t change the difficulty setting, press pause or set anything on automatic. There's a puzzle that I'm stuck on and it's fucking hideous. None of this works well in the single-player mode, and I don’t know how to unlock party members. I don't like this game any more. It's really hard.” His breath catches in his throat. He leans his head on Taiju’s stone shoulder and closes his eyes. ”There aren’t even any talking NPCs in it. Who does that? Every self-respecting game should have some NPCs. I’d give a lot for three or four boring lines of endlessly cycling dialogue right now. If you could speak, I bet you could make up some really annoying ones.”

The sun slowly rises. It climbs up to zenith and brings with it the pleasant warmth of an early autumn afternoon. He dozes off at some point and starts awake when a bird takes off, calling as it goes. His hand jerks painfully in place; his fingers are still stuck between Taiju’s petrified ones.

He feels more clear-headed. Those three cups of water finally seem to have done their job, and he's really hungry now. When was the last time he ate? Was it the handful of berries he stuffed in his mouth yesterday morning between two experiments? What about before that? He thinks back and concludes that the last time he ate a full set of meals was several days ago. His meal schedule had gotten more and more erratic, and towards the end of it, he even forgot to drink.

He's been focusing on the experimenting at the expense of everything else. He has overworked himself. It’s a simple mistake, and an amateurish one. Luckily, it's also one he can easily fix.

He extricates his hand, climbs out of the pit and dusts himself off. Then he turns back to Taiju. ”Just so you know, we’re not going to talk about this ever again. Understood?”

There’s something red glistening on Taiju's hand. That's the hand he was holding. He looks at his thumb.

The wound has cracked open and a small trickle of blood runs all the way down to his wrist. As he looks at it, he becomes aware that his thumb is still throbbing. That means it’s probably infected. He needs to dump some disinfectant on it, maybe even get a prescription—oh, wait. He has neither disinfectants nor antibiotics here.

Food and drink will have to wait: dealing with this is now his top priority.

-

After going through and discarding several options, he ends up using a boiled, hot chert sliver to sterilize the wound. It hurts like hell, but at least the bleeding stops. A few hours later, the throbbing starts to fade, too.

Over the next couple of days, he pulls strips of bark off willows and boils them until he gets a dark brown infusion, which he uses to rinse the wound every few hours. He also drinks copious amounts of it – it tastes like crap – and tries not to touch anything with his injured hand. Every night before he goes to sleep, he wraps the thumb loosely in a clean strip of leather, and every morning after he wakes, he boils that strip and sets it out to dry. It six days, but finally the redness and puffiness fade and the skin starts to show signs of knitting itself back together.

_Note to self: next time you want to write something down, you idiot, get a lump of coal._

**Notes for the Chapter:**

> Content warnings:
> 
> \- An infected wound  
> \- A panic attack, disorganised thinking, emotional instability and an instance of self-harm (as seen in canon) brought on by isolation and stress
> 
> Senku is really sad in this one. I'm sorry I did this to him.


	12. In Case Of Emergency, Pull Out The Rules

**Summary for the Chapter:**

> It's always darkest before dawn.

Something good comes out of it, at least: Senku establishes a steady daily routine to prevent any repeat incidents of _it seemed like a good idea at the time_. He gets up in the morning, fetches fresh water if he needs to, filters it, eats breakfast, does experiments for a few hours, has a snack, goes out to forage and to check the traps, eats dinner, experiments some more or goes to check on Taiju or Yuzuriha, gets back before it gets dark, has a snack and goes to bed.

”Failure is an important part of progress,” he tells Taiju as he sits on the edge of the pit and sips cold willow tea from the jar he brought with him. ”I know that. You know that too, don’t you? Remember how many times our rockets blew up before we got one up into mesosphere, and then that one blew up too?”

What’s new about it is the _sheer amount_ of failure involved when you can’t look anything up and the things you have to work with boil down to fire, flint, clay, sand, water, wood, straw, a bunch of rocks you’ve found lying around, nitric acid, bat guano, occasional animal carcasses, memory, your hands, and trial and error. That sounds like a lot, but it _really_ isn’t. His respect for people who had to operate in the world before writing was invented has rocketed sky-high.

He sighs. ”That’s just the way it is. You find nine, ninety-nine, or nine hundred ninety-nine ways that don’t work, before you find the one that does.”

-

 _Nine thousand, nine hundred ninety-nine attempts_ , he thinks that night, squeezing his blanket tightly. _Ninety nine thousand, nine hundred ninety-nine attempts._ _Nine hundred ninety-nine thousand, nine hundred ninety-nine. Nine million, nine hundred ninety-nine thousand, nine hundred ninety-nine. Ninety-nine million, nine hundred ninety-nine thousand..._

He doesn’t need to count anything right now. What he needs is to stop listing out numbers on a logarithmic scale and go to sleep.

 _One, two, three, four,_ _five, six_ _—_ stop. _Stop!_

He turns to his side, pulls the blanket over his head and stays under it, keeping his breathing deliberately slow and steady, until the rising concentration of carbon dioxide in there forces him to come back out. He takes one, two, three, four deep breaths.

Counting was what kept him awake and overwrote any major changes that being conscious might have made to his brain, but...

What if counting was also what had kept him _alive?_

-

He’s up before dawn and he hasn’t slept a wink. A reasonable course of action would be to go back to bed. Instead he’s walking swiftly towards the cave with the shovel on his shoulder.

It takes a while to dig Taiju out entirely. He’s heavy; Senku needs to use the handle to lever him out of the pit. It bends and creaks ominously, but it holds. The next issue presents itself once his friend is back on his feet: Senku can barely lift him off the ground for a couple of shaky seconds if he wraps his arms around Taiju’s waist. He can’t walk like that. Taiju is too heavy for him to drag without the risk of damaging him. He’s still not sure how much force it takes to break someone who is petrified, and it’s not something he’s willing to experiment on.

He manoeuvres himself around Taiju until they’re back to back. If he stays in a crouch and gets most of the weight on his back, he might be able to move him. The problem is that he can’t get a proper grip, so when he takes a step forwards, Taiju’s feet stay put and he starts to slide off Senku’s back.

Taiju’s arms are up too high. His waist is too smooth. The only handholds Senku finds turn out to be the grooves under his ass. Digging his fingertips in there gives him enough traction to slowly inch them forward, and his grip only slips every couple of steps.

He can’t believe that the first time he puts his hands on someone’s taint is by accident and involves _Taiju_. If he believed in some kind of fate, he would say that someone somewhere owes him big for this.

It starts to rain.

-

After what feels like forever but is actually 1,278 seconds, Senku dumps Taiju face-first into a pile of guano. The lazy bastard deserves it. He should have gotten up _ages_ ago.

He’s awake. He has to be. He's awake, and all he needs is more nitric acid. He’s just as stubborn and tenacious as Senku himself is. He's Senku's brother from another mother, sharing that same streak of sheer, unreasonable persistence. They’re two peas in a pod. He has to have held on. If he’s faded, if he’s _gone_ and Senku can’t wake him up...

Believe. He has to believe. He has to wait, and he has to believe. _He has to_.

His throat feels rough. Has he been shouting? How does he not know that?

Outside, lightning flashes. It's harsh and it's loud and he _can't do this any more._

”I can’t do this without you, Taiju! Come back!”

Taiju, being petrified, neither moves nor says anything. The same way he hasn't moved a millimetre or let out the tiniest noise every single time Senku has come here to see him. He's still and he's silent and he's _stone_.

Trees sway in the wind outside. Inside, nothing moves. Despite the weather and his yelling, even the bats are huddling up there quietly. The rain isn’t loud enough to drown out the sound of his ragged breathing. It echoes in his ears, getting louder with each breath he draws. The walls of the cave are slowly falling in on him.

Senku turns on his heel and flees. Rain pelts him hard enough to soak through his clothes almost immediately. It's cold, and it jolts him back to his senses.

He comes to a stop by the shallow ditch he lined with river stones. Water is already gathering at the bottom.

This is where he broke out. It follows from that that breaking out _is_ possible. There are rules to it. _There are_ _rules_. Even the data points that originally looked like deviations become part of the pattern once you amass enough data.

He isn’t an outlier. He isn’t an anomaly. _He isn't different_. Never in his life has Senku wanted this badly to be average.

He stands in the rain with his arms wrapped around himself and shakes. The water is cold. He’s cold because of the water. The water is cold and it rains all over him. It's made his face wet. His face is wet. He's crying. He's crying, and he's shaking, and it rains. _Fuck_.

It's the stress. He's under an unhealthy amount of stress. The stress is getting to him because he didn't sleep. That’s the only explanation he can handle right now without crumbling under the weight of it all.

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- More disorganised thinking and emotional instability  
> \- A full-blown freak-out about being alone in the world


	13. Might Be That It's Monday, Might Just Be Me

**Summary for the Chapter:**

> Trans Boy Scientist Uplifts Japanese Macaques Into Stone Shovel Age, Founds Cult of Ditch Man

The downpour has turned into an endless drizzle by the time Senku stumbles back to the tree house. He forgets to take the shovel; he realises that he doesn’t have it with him when he tries to put it back where it belongs. He doesn’t remember where he left it.

Oh well, it’s not like anyone will steal it, because there’s no one around but him and deer and some bats and the monkeys.

If the monkeys steal his shovel, maybe they do so because they’ve watched him long enough to learn how to use it. In that case, they deserve to have it. When he starts tripping over shallow, monkey-shaped pits lined with rocks, he'll know for sure. _Trans Boy Scientist Uplifts_ _Japanese_ _Macaques Into Stone Shovel Age, Founds Cult of Ditch Man_. That would make for good clickbait, or a tongue-in-the-cheek chapter title for his biography. He just needs to depetrify someone who can write it, reinvent paper, reinvent ink, reinvent a printing press, and then depetrify people to read it. No big deal. He’ll get it done by Monday, whenever that is. He has no idea what weekday it is today. There's probably a way he could find out, but he never bothered to learn it, and _poof_ , now it's gone bye-bye and there's no more weekdays for anyone any more.

He forces himself to choke down two handfuls of nuts and some water even though it feels like they want come right back up. Gotta remember to eat and drink. His soaking wet skirt sticks to his skin, and when he peels it off, it feels like it takes half his epidermis with it. He drops it on the floor, where it lies in a heap. He stares at it. Then he stoops to pick it up and spreads it on a branch hanger.

His teeth chatter by the time he crawls under his blanket and pulls the one he’s been making for Taiju on top of it. Gotta be careful not to catch a cold. You can’t catch a cold from just being cold, because getting a cold because of being cold just means rhinoviruses getting a leg up because your body temperature goes down. Except there’s no people for him to catch rhinoviruses from. Though there's probably a metric shit ton of their cousins in the bats, so he's not exactly home safe. Bats are highly social and have a hypoactive immune system, which means they're chock-full of fucking everything virulent under the sun, and yet somehow they don't get sick from it like humans do. If he's caught something from them, he's probably going to die.

Could bats catch the petrification virus and act as a reservoir species for it? Could viruses survive in the stone for millennia? No, that's ridiculous. Is it? He doesn’t know jack shit about this. Who knows, maybe after you're petrified you become a permanent carrier, like with chickenpox or herpes. Or maybe it's a retrovirus like HIV, and incorporates itself into your DNA. Compromising his immune system could mean that the petrification viruses start proliferating in his cells again, which means that he will wake up petrified... if he wakes up at all. If he's petrified while he's asleep, that's probably it for him.

It’s not that bad. That's just a particularly nasty scenario. Even if he does experience a flare-up and gets turned back into stone, sooner or later Taiju is going to break out. He’s awake in there. He is. Believe, Senku. Wait and believe.

If Senku gets repetrified, Taiju will wake up and find the tree house. Taiju will find him. The big oaf will have everything that Senku has made, and it will get him through the winter. Taiju will think of something. He reasons at the pace of a particularly slow glacier, but he’s super reliable. They might end up a couple of years apart in age because of how long it will take for the oaf to figure out the nitric acid, but what’s a few years between friends? Though if it’s more than twenty, he will kick Taiju’s ass. The big oaf will probably also do something unbelievably stupid in the meantime, like try to make bungee cords from vines or eat the bats, and then Senku will have to yell at him.

All he needs to do is to stay conscious. Just in case. He's so very, very tired, but after 3,700 years of practice, fighting the impulse to nod off should be a breeze...

**Notes for the Chapter:**

> Additional content warnings:
> 
> \- Senku is still off in this one, and he starts to think about bat pathogens again  
> \- Fear of going to sleep and never waking up


	14. If You Repeat Something Often Enough

**Summary for the Chapter:**

> Fact number two: He had another, uh, stress-related incident yesterday.

Morning dawns, peach-coloured and bearing with it the first hints of autumn crispness. A bird sings outside. It’s the same one that often wakes him up in the morning; he knows it by the sound.

Senku peels his lids back and blinks blearily at the ceiling. It’s still dim inside the tree house. Good, at least the light is not a problem this time.

He pushes himself up to a slouch and rubs at his eyes. The first thing he takes note of is the crumpled mess that is supposed to be his clothes hung out to dry. Great, now he’ll have to put up with unpleasant damp patches all day.

Get up. Fetch water. Filter it. Wash your face. Eat and drink.

Once he sits down with his perishables basket, the bird that woke him up flies down to have a look. He has no idea what species it is, but it’s considerably bigger than a swallow and has a black head, grey wings and a speckled white chest. Some kind of a thrush, maybe. It likes to sit on the roof of his lab and warble.

He tosses it a berry and watches as it dives after the small orb. It pokes at it a few times with its beak and then looks at him with its head cocked.

”That’s all you get,” he tells it. ”I’ve got to lay out all my facts and look at them, and my brain needs calories. Get your own food.”

The bird hops around him hopefully for twelve more seconds before it sees something and dives after it. He watches it pick up a worm and gobble it down.

Fact number one: He’s not petrified. Latent petrification virus reactivation hypothesis is probably a bust. Well, it was a pretty dumb one. It was pretty dumb, and couched in a whole lot more of pretty dumb. At least no one else was around to witness that.

Fact number two: Related to the above, he had another, uh, stress-related incident yesterday.

Fact number three: Something must have thrown him out of balance and set it off. What was it this time? He has eaten regularly. He hasn't overworked himself. The most likely culprit is sleep, because he didn’t get much of it two nights ago. How well had he slept before that? Probably not well enough.

Sleep is essential. You miss out on it often enough, you start to get a little unhinged. It's not something you should skimp on if you can help it. _Rest is part of working_ , like dad sometimes says.

He could try to find some edible grasses to give his brain more carbohydrates to make serotonin with, or traditional sleeping aids like valerian with some semblance of proven effectiveness. He could also try some good, old-fashioned sleep hygiene and motivational self-talk. After all, he wants to be in decent shape when Taiju wakes up. If doesn’t look after himself, Taiju will notice and start to fuss, and they both know that will lead to unsolicited physical contact, which in turn will lead to general aggravation and possibly yelling.

He also needs to be in shape because once he’s up, Taiju will probably also need comforting over the fact that he put off confessing his love for Yuzuriha for five years only to get delayed for another four thousand. If the first person he meets is a gibbering, sleep-deprived wreck, that’s going to be no help for him at all.

Which reminds him—

Fact number four: Taiju is not going to appreciate waking up face down in a mound of guano. It’s really not healthy, either. Senku is going to have to skip his morning experiment session and provide him with better bedding.

He gets his knife and some rope, stuffs his dinner into a bag, and sets off for a grassy meadow he remembers seeing upstream.

It takes him four trips to haul enough grass and reed to the cave that he's satisfied with the result. He drags Taiju back to his feet and props him against the wall. The shovel turns out to be right outside, leaning on a tree. He takes note of where the nitric acid falls, moves some guano out of the way, lays the bedding down, and with a lot of heaving and grunting and some rather inventive swearing, deposits Taiju onto it.

”You’d better appreciate this,” he tells the stone oaf as he sits down next to him and wipes bits of grass off his sweaty face with his arm. ”Even I don’t have it this comfy.”

-

He decides to skip the second stretch of experimentation on his daily schedule as well. Everyone needs a day off every now and then, especially when they’ve recently been tired enough to start inventing hypothetical horrible fairy tales to add to the already existing horrible fairy tales.

He wanders back to the river, washes his hands as best he can, and then digs some mushrooms out of a bag and sits down on a rock, munching slowly on them.

He’s going to check on Taiju more than once a day now, but if his friend breaks out on his own, Senku probably won’t be around to see it. That could pose a problem.

Then he gets an idea.

-

”I know with ten billion percent certainty where the big oaf is going to head after he wakes up,” Senku tells Yuzuriha as he carves letters into the camphor’s trunk next to her. ”I’m going to leave him a message here, so he doesn’t wander off like an idiot. I don't have time to go looking for his lost ass.”

Yuzuriha stands there with her hand held up like she always does, a worried look on her face.

He touches her lightly on the arm. ”Don’t worry, I’ll come get you too soon enough. I just need Taiju first. Besides, he’s got something to tell you that he’s been meaning to get off his chest, and we should give him a head start with that. You and I already know how you feel about him, but he takes forever to get his head around these things, so he can use all the help he can get. And even if I could drag you all the way to the cave from here, you and I wouldn’t really make half as effective a team as either of us would with him, and you would agree with that assessment if you could. So...” he hesitates. ”Hang in there, all right?”

He climbs back down, feeling a bit foolish. He’s been talking at her enough to get over any residual embarrassment about it, but telling her that now felt strangely like he had been expecting her to answer, even though he knows she can't hear him. Even if she were awake in there, it's not like she could let him know.

Why _wouldn’t_ she be awake? Why does it sound self-evident to him that she’s not?

It's because she’s reasonable. She isn’t as stubborn as Taiju is, or as driven as Senku himself is. She doesn’t have an overarching goal that she’s tirelessly working for, nor an unfair amount of energy that would keep her going long past the point where doing so made sense. Yuzuriha knows when to quit. She would have let herself fall into unconsciousness and spared herself the trouble.

He’s not sure what it says about him that he didn’t.

Yuzuriha would have faded. That means he has a new imperative: to find a way to revive those who aren’t conscious any more. It must be done, it can be done, and somehow, although he has no idea how as of yet, it _will_ be done. He has time and he has science; he _will_ figure it out.


	15. Chapter One Complete. Save Your Game?

**Summary for the Chapter:**

> Good night, world. Science man Senku will get back to saving you in the morning.

On his way back from the camphor copse, Senku stumbles – quite literally – over a large, moss-covered, vaguely rectangular rock. Further examination turns up several more like it in the immediate vicinity. They look like they might have served as the foundation of a building at some point, or maybe they had been part of a stone wall. When nothing more turns up, he starts walking again.

Large stone foundations, like those of an old castle, could still be whole enough to be recognisable. Finding them under all this plantlife would be the hard part. It would be like looking for needles in a haystack. It would be one thing if he had technology like drone-mounted LiDAR laser scanners that could see through the foliage and 3D mapping software to make sense of the readings. Though even if he did, he would still probably find very little. Stone lasts long enough to still be recognisable as man-made after all this time, but steel-reinforced concrete had been the go-to building material of modern civilization. Even the best of that would have crumbled away after a few centuries. Concrete just isn’t that durable in the long run.

There’s one exception to that rule, of course: _opus caementicium_ , the famously long-lasting concrete that ancient Romans made with volcanic ash. It resists cracks to begin with, and when it’s exposed to seawater, it becomes tough as hell. Leave it in the sea for two millennia and when you go check, it’s still there. It’s the strongest construction material humans have invented in two million years. Still, super-duper long-lasting concrete had been even less common in modern-day buildings than stone, and he would hardly find anything useful even if he could pinpoint—

His steps slow, until he comes to a halt.

 _Opus caementicium_ becomes more durable when sunk in sea water because a chemical reaction happens between the sea water and a mineral called phillipsite that's found in the volcanic ash that the Romans used to make their concrete. The reaction alters and extends the phillipsite’s crystalline structure, turning it into the even more durable tobermorite. That’s why sea walls made with Roman concrete last for thousands of years and only get tougher with time.

As implausible as it sounds, perhaps whatever causes the petrification works on bodies like sea water works on phillipsite. Perhaps it turns something in them into the durable crystalline lattice structure he already thought of, like that of diamond or beta carbon nitride. If it does – and here's clincher – it wouldn't start in _just one spot_.

If the petrification involves a crystal structure, and its crystallisation process doesn’t spread out uniformly from a single point in an affected body, there should be grain boundaries where different areas of crystallisation, or grains, meet and aren’t quite aligned with each other. If there is a crystal structure, and it isn’t completely homogeneous, that means that grain boundaries will occur. It’s a simple scientific fact. A really simple, rudimentary scientific fact that he only thought of just now.

This is embarrassing. This is _beyond_ embarrassing. This is exactly the kind of thing that happens to you when you work too hard and don't sleep enough.

Not only are grain boundaries areas where differently aligned sets of atoms meet, but they're also where the impurities get pushed. That makes them weaker than the grains. Acid etching of metals takes advantage of that: it breaks the separate grains apart by washing those impurities away. Could that work with lattice crystallisation, too? Instead of simply eroding the matter in between, could it undo the crystallisation itself?

Nitric acid revived him, but so far it hasn’t revived anyone else. He was conscious, and consuming something in the stone to fuel his brain. Maybe what he was consuming came from the grain boundaries, and taking it out left them weak enough for the nitric acid to chomp down on the rest of what was there. By using energy to think, he could have quite literally been putting pressure on the petrification at its weak spots.

He starts walking again, tapping a finger against his lips.

Nitric acid might not be enough for less destabilised grain boundaries, but it’s far from the only substance that affects them. There’s a whole list chemicals used for acid etching.

One such etching agent can be made by combining copper sulfate with salt. The sulfate would require sulfuric acid, copper and electricity to make, so that one’s a nope for now, because he doesn't have magnets or chemical battery materials.

Then there’s hydrochloric acid – also known to its friends as stomach acid – which is more accessible, because making it takes iron, sulfuric acid and salt, or even just salt and sulfuric acid.

Sulfuric acid is the tough part. He would need to make a gas absorption system, too, and for that, it would be really, really good to have glass. In any case, it’s looking like he’ll be making a trip to find some volcanic springs. The nearest ones would be at... Hakone? That’s some eighty kilometres away. Better get serious with that sextant he’s been playing with.

The fundamentally important thing here is that he knows how to make all these things, and that the materials for them should be available in the environment. It’s going to be a pain in the ass and and it will take a small forever, but now he has something to work with. Now he has a betterhypothesis, one that's actually testable. At worst he’ll have to sink a couple of years into it, but hey, what’s a few years between friends? And if he gets too impatient, he can always throw up on Taiju in the meantime and see what that does.

-

Senku lies on his back in the tree house, arms crossed behind his head, right above that bit of stone that’s still stuck to his neck. His ankle itches and he’s been trying to sleep for nearly twenty minutes, because sleep is important, damn it, but he can’t seem to stop thinking about acid etching.

If he makes hydrochloric acid, he could combine that with the nitric acid to make aqua regia, the king of acids that is strong enough to dissolve gold. Not that gold is likely to be present in petrified people in any significant quantities—

The nitric acid. He already has nitric acid.

Nitric acid, combined with ethanol, makes nital. Nital is a hardcore etching agent. Nital could be _just the thing_ for this.

Alcohol is a much older discovery than iron, and it’s ten billion percent easier to acquire than sulfuric acid. All he really needs is time and something to ferment.

Pleased with himself, he turns to his side, yawns and huddles down into the sleeping bag. Good night, world. Science man Senku will get back to saving you in the morning.

For the first time in what has been too long a while, he sleeps peacefully, and when he wakes, he feels refreshed.

-

Senku is up in a tree, looking for the straightest branches he can find, when Taiju comes running along beside the stream. His friend’s dumb, flesh-coloured mug is the best thing he has seen in half a year.

The oaf is stark naked except for some leaves, and he lunges straight at Senku. He's suddenly vividly reminded of trying to hold onto Taiju’s petrified ass, and he reflexively boots Taiju in the face and yells at him to get off, because he is _not_ having _that_ anywhere _near_ him again.

They’re still in a stone world and the civilization-building game is still stuck in the hard more, but now there are two players, and somehow that makes things ten billion times better. In fact, it makes them _exciting_.

**Notes for the Chapter:**

> This is the longest fic I've completed to date, and boy, has it been a ride. The amount of googling involved in the writing of it was preposterous. When I started working on this, I didn't understand chemistry at all. I learned a lot, and somewhere along the way, I also started randomly messaging my friends to say things like ”Hey did you know that corundum is actually aluminium oxide, which is just aluminium hydroxide without the hydrogen, which in turn is kinda like lye actually except with three hydroxyl groups instead of one and aluminium ions instead of sodium or potassium ions. I wonder if you could make aluminium soap?” Senku is the hardest damn character I've ever tried to write and I adore him.
> 
> Apologies for all the times that bat viruses pop up. I may have been blowing off some COVID-19 related steam there. 
> 
> A big thank you to everyone who reads all the way to the end! <3


End file.
